However, I have been rooting for a secondary team (in this case, my brother's team in the 49ers) just to give me something entertaining to watch on Sundays.

That's kind of the same thing I've been doing the past couple years. I haven't really had a specific second team I root for, but there's specific players that I'll root for (like Ray Lewis before he retired or RG3 for example). But I think I might adopt the Seahawks as a second team this year just because they're going to be so fun to watch.